I was given a 12.5HP Briggs short block engine. It was locked up in the cylinder. I managed to take it apart & free the piston. after examining it, it looked repairable. I cleaned all the parts & piston, & put in rings from a different engine of the same type, then honed out the cylinder (no damage, only bad carbon deposits). I wanted to know if it will run before putting any more money into it. I didn't remove any valves, just cleaned cabon deposits around it the best I could. then put it all back together.

I started it up & it runs & sounds really smooth with lots of compression & power, I cut all my grass with no problem at all, but it smokes like a freight train.

What do I need to do or replace in order to stop the smoke?

 

It depends. If the cylinder has any scratches to speak of in it, then it won't stop. Rings normally stop the smoking if the cylinder is ok. Proper cross-hatch honing pattern is also needed to properly seat the rings.

 

On a flat head engine, the three areas that would cause an oil smoking situation are: 1- Worn cylinder; acurately measure to determine if it would need to be bored oversize. 2- If the cylinder is within specs then worn rings; place each ring a 1/4" in the cylinder bore and check the endgap. 3- Sloppy valve guides; check for side play of each valve while in the full open position.